Fix inferred type of async_sessionmaker

Improved the typing for :class:`.sessionmaker` and
:class:`.asyncsessionmaker`, so that the default type of their return value
will be :class:`.Session` or :class:`.AsyncSession`, without the need to
type this explicitly. Previously, Mypy would not automaticaly infer these
return types from its generic base.

As part of this change, arguments for :class:`.Session`,
:class:`.AsyncSession`, :class:`.sessionmaker` and
:class:`.asyncsessionmaker` beyond the initial "bind" argument have been
made keyword-only, which includes parameters that have always been
documented as keyword arguments, such as :paramref:`.Session.autoflush`,
:paramref:`.Session.class_`, etc.

Pull request courtesy Sam Bull.

Closes: #8842
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/8842
Pull-request-sha: fa6d1a8468e98b40e12f82ed7ddaddc1fde060ac

Change-Id: Iaaabc4572a87489d61617d970f62b9b50db4fac7

1 files changed, 24 insertions, 0 deletions

diff --git a/test/ext/mypy/plain_files/sessionmakers.py b/test/ext/mypy/plain_files/sessionmakers.py
index ce9b76638..2d02f2a3f 100644
--- a/test/ext/mypy/plain_files/sessionmakers.py
+++ b/test/ext/mypy/plain_files/sessionmakers.py
@@ -86,3 +86,27 @@ def main() -> None:
     sess = scoped_fac()
     # EXPECTED_TYPE: MySession
     reveal_type(sess)
+
+
+def test_8837_sync() -> None:
+    sm = sessionmaker()
+
+    # EXPECTED_TYPE: sessionmaker[Session]
+    reveal_type(sm)
+
+    session = sm()
+
+    # EXPECTED_TYPE: Session
+    reveal_type(session)
+
+
+def test_8837_async() -> None:
+    as_ = async_sessionmaker()
+
+    # EXPECTED_TYPE: async_sessionmaker[AsyncSession]
+    reveal_type(as_)
+
+    async_session = as_()
+
+    # EXPECTED_TYPE: AsyncSession
+    reveal_type(async_session)